1. Field of the Invention
The present invention relates to radiation imaging systems. More particularly, the invention relates to a protective cover for an x-ray imager suitable for use in medical diagnostic applications. A method of attaching the cover to the upper surface of the x-ray imager""s substrate is also provided.
2. The Prior Art
A number of protective covers for radiation imaging systems used for medical and industrial purposes are known. For example, U.S. Pat. No. 5,132,539 to Kwasnick et al. relates to a planar x-ray imager having a moisture-resistant sealing structure.
Such sealing covers are desirable to protect the scintillator material of the imaging system from moisture absorption. The covers are especially desirable when the end use environment has a high humidity content. For example, cesium iodide, a common scintillator material, is hygroscopic and exhibits a tendency to absorb moisture from the atmosphere around it. In so doing, the material becomes hydrolyzed with a consequent degradation in its luminescent properties. In radiation imaging systems, the radiation typically comprises x-ray or gamma rays. This radiation is absorbed in the scintillator material, resulting in the generation of photons of light. These photons in turn are detected by photodetectors to generate an electrical output signal. This signal is processed to drive a visual display device or other equipment to analyze the detected electromagnetic radiation patterns. Chemical reactions occur continually between the cesium oxide scintillator and the atmospheric moisture of the radiation detector""s end use environment. These reactions lead to the degradation of the detector resolution. They also lead to the deterioration of the conversion factor and the decline of detector/device reliability.
Known digital x-ray detectors employ a cover/epoxy seal/x-ray imager interface to isolate the detector""s scintillator from atmospheric moisture. The x-ray imaging device includes a photodetector array disposed on a substrate with a scintillator disposed on the substrate. A cover is bonded to the substrate with an epoxy bead so as to extend over the scintillator.
This existing cover/seal/substrate interface construction allows some ambient moisture penetration through the epoxy bead driven by moisture diffusion through the epoxy. Moreover, the process of cover attachment to the substrate suffers from a lack of consistent and repeatable output. The attachment process requires extensive and complicated process fixtures. It also requires a high degree of manual dexterity, and a process duration of 48-72 hours.
Hence, a cover and attachment method is needed that will reduce moisture penetration into the cesium iodide array from diffusion.
A radiation imaging device is provided with a cover/imager substrate interface to isolate the scintillator from the end use environment. The device includes a scintillator comprising a moisture sensitive material, such as cesium iodide. A photodetector array comprising a plurality of photodetectors is disposed on an imager substrate. A cover is hermetically bonded to the substrate with a sealant. The cover is generally in the form of a xe2x80x9cpicture framexe2x80x9d or open-ended box. The cover has first and second surfaces and a third surface connecting the first and second surfaces. The cover comprises a material being substantially impervious to moisture and having a low degree of radiation attenuation.
A method of attaching the protective cover to a radiation imaging device is also provided. In accordance with this method, the cover is disposed on the imager substrate to surround the scintillator. A curable sealant is then applied continuously along the outer surface of the cover. The sealant is then cured to hermetically bond the cover to the substrate.